1. Field of the Invention
The present invention relates to a method of manufacturing a multilayer ceramic electronic component, and more particularly, it relates to an improvement in a step of exerting pressure for increasing density of a ceramic laminate which is obtained by stacking a plurality of ceramic green sheets.
2. Description of the Background Art
A multilayer ceramic capacitor, which is an example of a multilayer ceramic electronic component, is manufactured in the following manner.
First, ceramic green sheets are prepared from a slurry containing dielectric powder, a binder and a solvent. Then, conductor films for defining internal electrodes are printed on predetermined ones of the ceramic green sheets, and a predetermined number of such ceramic green sheets are stacked to provide a ceramic laminate. Then, a pressure of several 100 kg/cm.sup.2 to several t/cm.sup.2 is exerted on the ceramic laminate at a temperature of 40.degree. to 90.degree. C., to increase density of the ceramic laminate. Thereafter the ceramic laminate is cut into predetermined dimensions, to obtain chips for independent multilayer ceramic capacitors. These chips are thereafter fired. Then, external electrodes are formed on both end portions of each chip, to obtain a desired multilayer ceramic capacitor.
The step of exerting pressure on a ceramic laminate which is included in the aforementioned method of manufacturing a multilayer ceramic capacitor is carried out in a step shown in FIG. 10, for example. A ceramic laminate 1 to be supplied with pressure is charged in a die assembly 2, and pressed through this die assembly 2. A rigid press or a hydrostatic press is employed for exerting such pressure. The die assembly 2 comprises an upper punch 3 which comes into contact with one major surface of the ceramic laminate 1, and a base 6 including a frame 4 which encloses the peripheries of the upper punch 3 and the ceramic laminate 1 and a base plate 5 which comes into contact with another major surface of the ceramic laminate 1 in a manner opposite to the upper punch 3. The ceramic laminate 1 is provided in its interior with conductor films 7 for defining internal electrodes. The conductor films 7 are formed to be distributed on central portions along surface directions of a plurality of specific ceramic green sheets forming the ceramic laminate 1, and overlapped with each other along the thickness direction of the ceramic laminate 1.
In the aforementioned step of exerting pressure on the ceramic laminate 1 through the die assembly 2, several disadvantages may result because a clearance is defined between the peripheral edge portion of the ceramic laminate 1 and the die assembly 2 and a portion of the ceramic laminate 1 provided with the conductor films 7 has a different thickness from those provided with no such films.
The ceramic contained in the ceramic laminate 1 which is compressed through the die assembly 2 along its thickness direction flows on the basis of its fluidity. Namely, the portion of the ceramic laminate 1 which is increased in thickness due to the provision of the conductor films 7 is so increased in pressure that the ceramic contained in this portion flows toward other portions that are not provided with conductor films 7 having relatively low pressures. However, although such flow is suppressed by friction in portions which are in contact with the upper punch 3 and the base plate 5 of the die assembly 2 respectively, the central portion along the thickness direction is free from such suppression and the ceramic contained therein flows easily and is moved a relatively large amount. Thus, those of the conductor films 7 which are located around the central portion of the ceramic laminate 1 along the thickness direction are extremely misregistered, as shown in FIG. 11. Referring to FIG. 11, symbol d denotes positional difference between the conductor films 7 resulting from such misregistration. This misregistration particularly remarkably appears in the conductive films 7 which are closer to end portions of the ceramic laminate 1.
Due to the aforementioned fluidity of the ceramic, further, the ceramic laminate 1 may be deformed along the major surface direction to degrees which are varied with the positions, in addition to the disadvantage shown in FIG. 11.
On the other hand, developments have been made in recent years to attain miniaturization and increase in capacitance of multilayer ceramic capacitors. In one of the countermeasures for such developments, an attempt has been made to reduce gaps d defined by internal electrodes 9 which are located in the interior of a multilayer chip 8, as shown in FIG. 12. However, if the conductor films 7 are misregistered as shown in FIG. 11, for example, the internal electrodes 9 provided by such conductor films 7 may be disadvantageously exposed on an undesired surface of the laminate chip 8 obtained by cutting the ceramic laminate 1, as shown in FIG. 13. This tendency remarkably appears as the gaps g shown in FIG. 12 are reduced. The internal electrodes 9 which are exposed on an undesired surface of the laminate chip 8 electrically conduct with both of external electrodes 10 and 1.1, to cause a failure of defective shorting.
When the conductor films 7 are misregistered, further, degrees of extension of the ceramic and the conductor films 7 caused by compression of the ceramic laminate 1 may be varied with the positions of the ceramic laminate 1, as hereinabove described. In this case, therefore, capacitance values are dispersed between a plurality of multilayer ceramic capacitors as obtained.